1. Field of the Invention
The present invention relates to a herbicidal composition for the control of annual bluegrass (Poa annua) comprising a microorganism belonging to the genus Xanthomonas.
2. Prior Art
Annual bluegrass which is grows abundantly on golf courses, city parks, athletic grounds and so forth is the most strong, harmful weed in the turf. This weed is widely distributed throughout the world. In particular, annual bluegrass mixed with the turf of golf courses, such as putting greens, tee grounds, fairways and roughs, propagates at all times in spite of frequent mowing, and scatters a large quantity of seeds into the turf all the year round. At present, there are a number of herbicides developed for the control of annual bluegrass.
However, abundant use of agricultural chemicals at golf courses has become a major social problem as overuse causes environmental pollution. Among currently used chemical herbicides, there is no foliar treatment agent which can selectively kill annual bluegrass mixed with American and European lawn grasses, such as bentgrass, bluegrass, ryegrass and fescues, without harming the desirable turfgrasses. Therefore, for the maintenance of bent green, manual weeding or even total renewal of turf is inevitably required, and the cost of which is tremendous.
Under such circumstances, the present inventor and others have developed and commercialized a herbicide (product name: Camperico Liquid Formulation) in Japan which comprises, as active ingredients, Xanthomonas campestris P-482 and P-484 strains and selectively controls annual bluegrass without polluting the environment.
In order for Camperico Liquid Formulation to work, the microorganisms contained therein must be contacted with fresh wounds of annual bluegrass immediately after mowing. Thus, frequently, there is disparity in effect depending on mowing conditions and uneven application. Even if a large-scale application has been conducted to avoid unevenness, most of the applied liquid formulation may drop off due to the wax layer on the surface of annual bluegrass and, thus, sufficient herbicidal effects may not be achieved. Although an attempt to use a sulfonylurea compound in combination with the Xanthomonas microorganism to improve the herbicidal effect has been made (Japanese Unexamined Patent Publication No. 7-187937), the chemical herbicide contained may cause phytotoxicity when applied to turf immediately after renewal or germination. Thus, this combination cannot be used at such times. Furthermore, in view of the possible environmental pollution which might be caused by the chemical herbicide contained, it is desirable to avoid this combined use.
As described above, Camperico Liquid Formulation developed by the present inventors still have various aspects to be improved, though it has an epoch-making effect as compared to conventional herbicides.